1. Field of the Invention
The present invention relates to a newly designed power module package, and more particularly to a high density power module package which is characterized in having the property of high heat dissipation, easy to fabricate the lead frame, and low production cost.
2. Description of the Prior Art
The conventional power module packages can be classified in three categories, namely:
(1) The first one is shown in FIG. 1A and FIG. 1B, wherein a high heat dissipation substrate 100 made of a high molecular insulation layer and a metal foil layer is prepared as a base substrate. All power pack module circuits and a plurality of chips 101, 102, 103 . . . are fabricated on the surface of the substrate 100. After that the module circuits and lead frames 121, 122, or the chips 101, 102 . . . and the lead frames 121, 122 . . . are electrically connected by wires 111, 113 . . . or by wires 112 . . . respectively utilizing wire bonding technique.
No matter how simple and easy to fabricate, the structure of the above described power module package has the following shortcomings:
1. Density of the power pack module circuits cannot be raised by reason that all the power pack module circuits and the chips are fabricated on the same substrate.
2. The foregoing shortcoming, described in xc2xa7 1 calls for a larger substrate to compensate for that leads to increasing the production cost.
3. The instantaneous heat conduction ability is poor since heat conduction relies only on the heat dissipation paste applied between the substrate 100 and the heat sink (not shown) which is formed on the outer surface of the substrate 100 for dissipating heat produced by those chips 101, 102 . . . on the power pack module circuits and being conducted to the substrate 100.
(2) The second example is shown in FIG. 2A and FIG. 2B, wherein a metal plate 200 is further attached to the bottom surface of the high heat dissipation substrate 100 for fabricating all the power pack module circuits and attaching chips 101, 102, 103 . . . on the substrate 100. Thereafter, the module circuits and the lead frames 121, 122, or the chips 101, 102 . . . and the lead frames 121, 122 . . . are electrically connected by wires 111, 113 . . . , or wires 112 . . . respectively utilizing wire bonding technique.
No matter how simple and easy to fabricate, and how advantageous in better heat dissipation by the metal plate 200 attached to the bottom surface of the substrate 100, the above-mentioned structure is unable to be released from the following shortcomings:
1. Density of the power module circuits cannot be raised by reason that all the power module circuits and the chips are fabricated on the same substrate.
2. The foregoing shortcoming described in xc2xa7 1 calls for a larger substrate for remedy that leads to increasing the production cost.
(3) The third example is shown in FIG. 3A and FIG. 3B, wherein the lead frames 121, 122 . . . are directly patterned on a metal substrate 200 integrally with the power module circuits and the chips 101, 102 . . . are also directly welded to (or using other means) to the lead frames. With this structure, there is established a heat conduction route for chips 101, 102 . . . lead frames 121, 122 . . . xe2x86x92 thin wall of the package materialxe2x86x92 metal plate 200 xe2x86x92 heat sink.
No matter how simple and( easy to fabricate, the structure of the above described power module package has the following shortcomings:
1. The density and precision of both circuits and overall structure of the power module package is restricted by reason that the lead frames and overall circuit patterns are integrally formed in one piece.
2. Efficiency of heat dissipation is limited by the fact that heat conduction of chips shall be en route to the metal plate by way of the package material.
In order to solve the above described problems, the present inventor carried out theoretical studies and simulating experiments. Based on these studies and researches, the present invention came to propose the present invention.
Accordingly, it is a first object of the present invention to provide a power module package in which the circuit density can be improved.
To achieve this object, the circuits are formed on a printed circuit board which is attached to lead frames, and chips are welded to the lead frames so that existence of the chips never affects the layout of the circuit pattern thereby improving the circuit density.
It is a second object of the present invention to provide a power pack module package whose substrate area is reduced to save the production cost.
To achieve this object, the circuit density of this power module package is raised.
It is a third object of the present invention to provide a power module package which has an excellent heat conducting property.
To achieve this object, a metal plate is attached to the rear side of the lead frame with a very thin insulation layer being intercalated therebetween such that the heat generated by the chips are rapidly and efficiently dissipated from the metal plate without being en route to the metal plate by way of the poor thermal conductive package material.
It is a fourth object of the present invention to provide a power module package which is able to withstand a very high temperature caused by an instantaneous huge current.
To achieve this object, the lead frames on the substrate are arranged in a planar configuration so as to facilitate heat conduction and assure a sufficient creepage distance thereby degree of product safety is greatly increased.